Breast cancer is a malignant abnormal cell growth in the breast. Cancer cells may spread to other areas of the body (called metastasis). Fibrocystic changes (e.g., formation of cysts, scar tissue) may cause benign (i.e., noncancerous) lumps in the breast.
In women, breast cancer is the second most common type of cancer and the second leading cause of cancer-related deaths. One in eight women in the United States will develop breast cancer during their lifetimes.
Approximately 200,000 women in the United States are diagnosed with breast cancer each year, and the disease causes about 40,000 deaths annually.
The incidence of breast cancer rises after age 40. The highest incidence (approximately 80% of invasive cases) occurs in women over age 50.
Most breast cancer develops in glandular tissue and is classified as adenocarcinoma. The earliest form of the disease, ductal carcinoma in situ (DCIS), develops solely in the milk ducts. The most common type of breast cancer, invasive ductal carcinoma (IDC), develops from DCIS, spreads through the duct walls, and invades the breast tissue.
Invasive lobular carcinoma originates in the milk glands and accounts for 10-15% of invasive breast cancers. Less common types of breast cancer include the following:                Inflammatory (breast tissue is warm and appears red, and tends to spread quickly);        Medullary carcinoma (originates in central breast tissue);        Mucinous carcinoma (invasive; usually occurs in postmenopausal women);        Paget's disease of the nipple (originates in the milk ducts and spreads to the skin of the nipples or areola);        Phyllodes tumor (tumor with a leaf-like appearance that extends into the ducts; rarely metastasizes; and        Tabular carcinoma (small tumor that is often undetectable by palpation).        
While sarcomas (cancer of the connective tissue) and lymphomas (cancer of the lymph tissue) develop in the breasts, they are relatively rare occurrences.
Approximately 5% of breast cancer cases have a genetic link that results from an inherited mutation in genes identified as BRCA1 and BRCA2. Patients who inherit an altered BRCA1 or BRCA2 gene have an increased risk for developing premenopausal breast cancer and are more likely to have family members with the condition.
The cause of breast cancer is unknown.
The diagnosis of breast cancer is made through a process called triple assessment, which includes:                1. clinical examination;        2. imaging procedures e.g., mammogram, breast ultrasound, magnetic resonance imaging (MRI scan); and        3. biopsy (surgical removal of tissue for microscopic examination) of a mass detected by physical examination or mammogram.        
There are various options for the treatment of breast cancer. They include surgery, radiation, immunotherapy, hormonal, chemotherapy, and radiation or one or more of the foregoing options in combination.
Surgery combined with radiation and/or chemotherapy is the most common treatment for breast cancer. The type of surgical procedure recommended to the patient depends on the stage of the disease. Mastectomy is the most commonly performed procedure.
Radiation uses high-energy x-rays to destroy cancer cells. Treatment is delivered by a machine outside the body (called external radiation) or by radioactive “seeds” that are placed directly into the tumor (called brachytherapy). Breast cancer is usually treated using external radiation.
Radiation may be used to shrink the tumor before surgery (called neoadjuvant therapy) or may be used after surgery to destroy cancer cells that remain in the breast, chest wall, or underarm (called adjuvant therapy).
Radiation therapy is performed in a hospital or an outpatient center. Each treatment lasts a few minutes and treatment is usually given 5 days per week, for 6 weeks. Side effects include fatigue, reddening of the skin and swelling.
Several drugs have been developed to treat breast cancer that is responsive to estrogen. Selective estrogen-receptor modulators (SERMs; e.g., tamoxifen, raloxifene) inhibit the effects of estrogen on breast cancer cells.
Tamoxifen (Nolvodex®) is taken in pill form, usually for 5 years after breast cancer surgery to prevent recurrence. After 5 years, patients taking tamoxifen have an increased risk for early stage cancer of the lining of the uterus. The most common side effect of this medication is hot flashes. Other side effects include the following: depression, dizziness, hair loss, headache, and swelling. Studies are being conducted to determine if raloxifene (Evista®) can effectively reduce the risk for breast cancer. Side effects include hot flashes and leg cramps.
Fulvestrant (Faslodex®) destroys estrogen receptors in breast cancer cells. It is used to treat metastatic breast cancer in postmenopausal women who have been treated unsuccessfully with tamoxifen. This treatment is administered once a month by intramuscular injection. Side effects include nausea, hot flashes, and weight gain.
Goserelin (Zolodex®) is a synthetic form of luteinizing hormone-releasing hormone (LHRH) that is prescribed to treat metastatic breast cancer in premenopausal women. This medication signals the body to stop producing estrogen, depriving the tumor of the estrogen it needs to grow. Several weeks are needed before tumor growth slows. Side effects include hot flashes, sexual dysfunction, increased pain, and rash.
Aromatase inhibitors (e.g., anastozole [Arimidex®], letrozole [Femara®], exemestane [Aromasin®] inhibit the action of the enzyme aromatase, which is involved in estrogen production in postmenopausal women. These drugs may be prescribed for postmenopausal women with advanced breast cancer that has been unsuccessfully treated with tamoxifen. Side effects include the following: cough, depression, diarrhea, dizziness, fatigue, headache, hot flashes, increased appetite, nausea and pain.
Chemotherapy is a systemic treatment i.e., travels throughout the body via the bloodstream, that often uses a combination of drugs to slow tumor growth and destroy cancer cells. Drugs may be administered orally or intravenously. Chemotherapy is often used as an adjuvant therapy to destroy breast cancer cells that have metastasized to the lymph nodes. It also is used to shrink the tumor prior to surgery (neoadjuvant therapy) and as a primary treatment.
The combination most commonly prescribed to treat breast cancer is doxorubicin (Doxil®) and cyclophosphamide (Cytoxin®). Paclitaxel (Taxol®, or the generic form, Paxene®) is often prescribed after this combination treatment, when breast cancer has metastasized to the lymph nodes. It is also prescribed following breast cancer surgery. Other chemotherapy drugs include docetaxel (Taxotere®) and gemcitabine (Gemzar®).
Side effects are often severe and include fatigue, hair loss (alopecia), fever, low blood cell count (e.g., anemia, neutropenia, thrombocytopenia), infection and nausea.
Biological therapy (also called immunotherapy) involves using trastuzumab (Herceptin®) to inhibit tumor growth and enhance the immune system's ability to fight cancer. It also may be combined with chemotherapy as a first line treatment for metastatic breast cancer and may be used after chemotherapy or anti-estrogen therapy to improve the effectiveness of the treatment. When used alone or in combination, side effects include cardiac dysfunction (causes severe cough, shortness of breath, difficulty performing physical activities), chills, congestive heart failure, cough, diarrhea, fever, headache, nausea, weakness and vomiting.
Despite the positive results obtained in clinical applications in chemotherapy, the search for new compounds and compositions is still open to the identification of new compounds with optimal features of reduced toxicity and increased tumor selectivity.